1. Field of the Invention
The present invention relates to a particulate material suitable for the removal of heavy metals from an aqueous effluent, a process for making the material and a system and a method for removing heavy metals from an aqueous effluent using the particulate material. 2. Description of the Related Art
Raw wastewater generated by industry and contaminated ground water contain substantial concentrations of metal ions, oxides, cyanides and other substances. Common pre-treatment techniques of wastewater or ground water typically involve flocculation, hydroxide or sulfide precipitation, clarification and pH adjustment of the water.
A number of in-line modifications of the usual pre-treatment techniques or substitution of less toxic oxidants or cleaners can be employed successfully to reduce or eliminate residual contaminants. However, these techniques often do not remove all the metals from the wastewater. Consequently, levels exceeding legislated discharge standards are common. Moreover, these techniques are often complicated and/or are expensive to employ.
Because of the large metal removal capacity and the natural abundance of peat, peat adsorption is potentially a cheap and effective technique for treating wastewater or contaminated ground water. Various chemical and physical properties of peat allow it to actively adsorb dissolved and colloidal metals from industrial effluents. Furthermore, peat can adsorb cyanide and other organic compounds from water containing heavy metals.
However, peat adsorption is not without its disadvantages. Peat, in its natural form, is composed of strands which are stringy and messy. Thus, natural or raw peat tends to be difficult to handle. Also, the hydraulic resistance of raw peat is high. Moreover, when packed in a column, the fines in the raw peat tend to be washed out, and the peat bed in the column tends to be compacted.
The Bureau of Mines has turned to the use of polysulfone as an encapsulant material for peat moss, as discussed by C. R. Ferguson et al. in "Biosorption of Metal Contaminants from Acidic Mine Waters", published in a paper at the 1991 Society of Mining Engineers (SME) Annual meeting, Feb. 25, 1991, in Denver, Co., and by E. M. Trujillo et al., in a paper entitled "Mathematically Modeling the Removal of Heavy Metals from a Wastewater Using Immobilized Biomass", published in Environmental Science and Technology, Vol. 25, No. 9, 1559-65 (1991).
Recognizing the high cost of polysulfone as an encapsulant, particularly for large quantity use in the field, whether bagged or for use in a packed bed column or a stirred reactor, an improved, a less expensive polymer encapsulant and a process for encapsulating peat in this polymer are needed. Ideally, such an encapsulant would also have good porosity in order to fully utilize the adsorptive qualities of the peat while imparting the needed structural integrity thereto.
Also, experiments have shown that enhanced ion exchange properties can be derived from materials with high peat loadings (.sup..about. 80% by weight of dry particulate solids), provided such loading does not exceed an encapsulants'ability to contain the peat. Thus, a particulate material having a high peat loading and a process for forming this material are needed.
Alternatively, it may be economical to utilize the adsorptive qualities of the peat without encapsulating it. Thus, there exists a need to enhance the adsorptive qualities of peat in its raw form.